Not to spoil the video or anything, but you take glow-in-the-dark powder, mix it in with printer ink, microwave it, suck it into a syringe, then inject it into an empty cartridge. Once it's printed, you can turn off the lights and see your hard work. As delicious as that glow-in-the-dark solution is when it comes out of the microwave, you probably won't want to drink it.